Organic thin film solar cells are solar cells prepared by disposing an organic photoelectric conversion layer between two different types of electrodes. Compared with inorganic solar cells typically using silicon, the organic thin film solar cells may contribute to substantial reduction of production costs and are attracting attention as a less expensive solar photovoltaic device.
Generally, a composition containing a conjugated polymer compound, a fullerene derivative and a solvent is used for the film forming of an organic film contained in an organic photoelectric conversion layer. Typical examples thereof include the composition disclosed in Non-patent Document 1, containing o-dichlorobenzene as a solvent, poly(3-hexylthiophene) as a conjugated polymer compound and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a fullerene derivative.    NON-PATENT DOCUMENT 1: Advanced Functional Materials, 2007, vol. 17, pp. 1636-1644